The CGIBD Gnotobiotic Animal Core is a highly visible resource that provides CGIBD members with germ-free (sterile) and selectively colonized mice to precisely study host/environmental interactions. This world-class facility has allowed CGIBD members, their trainees and collaborators to perform cutting edge investigations in wild type and genetically engineered gnotobiotic mice in the absence of microbiota (germfree) or colonized with single bacterial species (parent strains and gene deletion/complemented mutants), defined groups of murine or human bacterial species or complex communities of commensal microbiota from human or experimental mice or humans (humanized mice) with dysbiosis to study disease pathogenesis. In the past 4 years, the combined core facilities at UNC-Chapel Hill and North Carolina State University College of Veterinary Medicine have provided 3,479 germ-free or gnotobiotic mice to 19 CGIBD members and 41 external scientists in the U.S. Approximately 70% of these mice have been used by CGIBD members. Our repertoire of gnotobiotic mice has expanded from approximately 6 strains at the last renewal to 29 strains that include wild t3T)e, knockout, transgenic and reporter mice. The Core's specific aims for renewal funding are: 1) provide germ-free (GF) or selectively colonized (gnotobiotic) wild type and mutant mice, their tissues and cells for CGIBD interdisciplinary investigators exploring host/environmental interactions; 2) Derive additional GF genetically engineered mouse strains for CGIBD investigators; 3) Provide technical assistance for CGIBD investigators; and 4) Provide limited gnotobiotic animals and tissues to unfunded new or established investigators with novel hypotheses to generate preliminary data for NIH or foundation grant applications.